In general, a gas turbine is configured to obtain a drive force by injecting fuel into air which is compressed at a high temperature with a compressor, generating combustion gas by causing combustion inside a combustor, guiding this combustion gas to a turbine, and thereby rotating the turbine. Moreover, in the compressor and the turbine, a predetermined amount of clearance (tip clearance) is set in a space between tips of rotor vanes arranged in a circumferential direction and a casing provided so as to surround these rotor vanes.
Since the temperature inside the gas turbine becomes high, the difference between the inside and the outside temperatures becomes larger. As a result, the casing is thermally expanded in an axial direction and a circumferential direction thereof and is deformed into an oval shape. Meanwhile, the rotor vanes are also thermally expanded and deformed outward in a radial direction. When the casing and the rotor vanes are deformed as described above, there is a risk that the tips of the rotor vanes contact with the casing and are thereby damaged. Accordingly, the above-mentioned clearance is formed by estimating in advance amounts of thermal deformation of the casing and the rotor vanes at the time of operation. Meanwhile, if the clearance is made larger in order to prevent the contact attributable to the thermal deformation, performance of the entire gas turbine is degraded. Therefore, in view of improvement in performance and improvement in reliability, clearance management or positional management of the casing for forming a predetermined amount of this clearance has become extremely important in recent years.
Thus, conventionally provided are a structure configured to form a predetermined amount of clearance by sequentially stacking each step upward while setting a central shaft of a gas turbine to be perpendicular, or a structure configured to form a predetermined amount of clearance by use of an eccentric pin which is unaffected by the amount of displacement even if there is displacement between casings, or the like. Such conventional vane tip clearance management structures for a gas turbine are disclosed in cited documents 1 and 2, for example.
Patent Document 1: Japanese Patent Application Laid-open Publication No. 2001-200705
Patent Document 2: Japanese Patent Application Laid-open Publication No. 2004-162536